Nature and extent of the burden and risks associated with participation, benefit and group relatedness: participants will complete a medical screening questionnaire (15-30 min) and will undergo a medical screening (45 min; 2 blood samples, a urine sample and an electrocardiogram). Informed consent will be obtained. All participants will be vaccinated with NicVAX or Placebo 5 times on day 0, 28, 56, 84 and 112 (4 weeks in between each injection) During the training session (Day 0; ±1,5 hour) the inclusion/exclusion criteria and baseline laboratory results will be reviewed to ensure that no changes to the participants health and eligibility status occurred since the Screening Visit. Participants will be randomized and receive either one dose NicVAX 400µ in 1 ml or a placebo intramuscular. The cognitive fMRI task will be trained in a dummy scanner, and questionnaires will be completed. Subsequent vaccinations (days 28, 56, 84 and 112) should be given in the alternating deltoid muscle. Participants will be observed for 60 minutes to monitor possible adverse events. Adverse events, vital signs and concomitant medications will be recorded. During each test session (days 133, 140) participants will complete 5 questionnaires (30 minute total) and will perform several cognitive tasks inside the fMRI scanner (scan session in total ~85 min). The last test session (day 140) three blood samples (5-8 ml each) will be taken for nicotine-specific antibody assessment and to monitor changes. In total the study will take 18 hours to complete. The participants will be paid 10 euro/hr as compensation. The risk of vaccination, fMRI scanning and of administration of nicotine 2mg gum (delivering a dose of approximately 1-1.5 mg nicotine to the bloodstream) is negligible for carefully screened participants. The nicotine specific-antibody vaccine has been clinically tested on several occasions; the safety profile was favourable. Local reactogenicity was generally mild to moderate and subsided spontaneously. Vaccinated subjects with the highest antibody levels (top 30%) smoked less cigarettes per day and reported a higher abstinence rate than placebo subjects, establishing proof-of-concept. The group receiving the vaccine could therefore in theory reduce smoking/exposure to tobacco smoke and have consequential health benefits.